Olfactory dysfunction in essential tremor versus tremor dominant Parkinson disease

•Essential tremor and tremor dominant Parkinson disease variant constitute the main causes of geriatric tremor.•Olfactory dysfunction is a consistent non-motor manifestations (NMM) of PD and and additional sign in ET patients.•Sniffin’ Sticks test as well as Olfactory bulb volume are valuable biomarkers that differentiate doubtful TDPD and ET cases. Essential tremor (ET) and tremor dominant Parkinson disease (TDPD) variant constitute the main causes of geriatric tremor which differentiation is not always an easy mission. The objective of this work was to study the olfactory performance in ET and PD patients for possible consideration as a differentiating biomarker. This study was performed on 36ET, 22 TDPD variant and 24 healthy controls subjects (HCS) submitted to extended n-butanol Sniffin’ Sticks test (SST) and olfactory bulbs volumetry (OBV). There were significant decreases in SST threshold, discrimination, identification and TDI variables in TDPD patients compared to ET and HCS. ET patients showed significant decrease in the same variables compared to HCS. Regarding OBV, there were significant decreases in TDPD patients compared to ET and HCS with nonsignificant difference between the 2-latter groups. Our results showed that TDI score of 25 can differentiate between TDPD and ET patients with sensitivity and specificity (94 %, 91 %) respectively. Olfactory assessment is a rapid, safe, and easily applicable biomarker that could differentiate TDPD from ET in doubtful cases.